Furthermore, it can be shown that the following conditions are satisfied [1]}:
\(\int {\rm d}\nu \left[\frac{\delta }{\delta \sigma (\nu )}\left(\frac{\delta s(\eta )/\delta \sigma (\mu )}{s(\mu )-s(\eta )}\right)\right]=\int {\rm d}\mu \left[\frac{\delta }{\delta \sigma (\mu )}\left(\frac{\delta s(\eta )/\delta \sigma (\nu )}{s(\nu )-s(\eta )}\right)\right], \quad \mu \ne \nu \ne \eta \, ,\) 
\(\frac{\delta s(\eta )}{\delta \sigma (\eta )}=0, \quad \forall \eta \; .\) 
